The Diabetes Control and Complications Trial and the United Kingdom Prospective Diabetes Study have documented unequivocally that improved glycemic control decreases the incidence and progression of microvascular complicatons of diabetes. The implementation of regimens to rigorously control blood sugar in diabetic patients has led to an increased incidence of severe iatrogenic hypoglycemic events that have limited glycemic management of diabetes mellitus. Recent antecedent iatrogenic hypoglycemia impairs the neuroende:rine and autonomic response to subsequent hypoglycemia - a disorder known as hypoglycemia associated autonomic failure - thus increasing the predisposition to severe hypoglycemia. It is not known whether antecedent hypoglycemia has more general effects on autonomic nervous system function. Impaired autonomic function is associated with increased mortality and morbidity in individuals with diabetes mellitus. If hypoglycemia induces generalized autonomic dysfunction it may further increase the mortality and morbidity associated with diabetes mellitus. The goal of this research is to understand the mechanisms of hypoglycemia associated autonomic failure. The proposed studies test the hypothesis that antecedent hypoglycemia not only impairs the counterregulatory response to subsequent hypoglycemia but also impairs cardiovascular autonomic function in non-hypoglycemic individuals. These studies will examine those markers of cardiovascular autonomic function that, when impaired, are associated with increased morbidity and mortality in patients with diabetes. Furthermore, we hypothesize that antecedent hypoglycemia causes a rise in serum cortisol and that cortisol activation of glucocorticoid receptors mediates the development of hypoglycemia associated autonomic failure. The specific aims for the proposal are to assess autonomic control of cardiovascular function following antecedent euglycemia and hypoglycemia. In addition, we will determine whether administration of a glucocorticoid receptor antagonist, mifepristone, prior to antecedent hypoglycemia improves the autonomic and neuroendocrine response to subsequent hypoglycemia in healthy men and women. Thus, the broad long term objectives of the proposal are to fully understand the mechanisms and consequences of hypoglycemia associated autonomic failure with the ultimate goal of finding an efficacious treatment.